In the prior art, in the servers and the personal computers, in order to radiate the heat generated from the semiconductor element efficiently, the semiconductor element is connected to the heat spreader through the thermally conductive sheet. As the thermally conductive sheet, indium sheets, silicone grease, or the like is used.
The heat spreader is fixed to contact the semiconductor element through the thermally conductive sheet. Moreover, the thermally conductive sheet needs to be able to absorb the warp or the like caused by the heat generation during the operation of the semiconductor element, and to transfer the heat efficiently.
However, in the case that an indium sheet as the thermally conductive sheet is used, the indium sheet may sometimes be detached at the interface due to the warp of the semiconductor element. Also, in the case that silicone grease as the thermally conductive sheet is used, the pump-out in which the grease is pushed outside by the thermal cycle, or the void is generated easily.
In recent years, the chip size has been increasing by the advancement in the performance of the semiconductor element, and a larger warp tends to be generated during the operation of the semiconductor element. Also, due to the trend for the multi-chip package of the semiconductor elements, a level difference sometimes is generated between a plurality of semiconductor elements. For these reasons, the thermally conductive sheet is desired which have higher thermal conductivity and also have flexibility and that can sufficiently absorb the warp and the level difference in semiconductor elements.
As the thermally conductive sheet having such properties, the technique that uses the carbon nanotubes have been proposed.
A related art is disclosed in Japanese Laid-open Patent Publication No. 2011-96978, and Japanese Laid-open Patent Publication No. 2012-224507.